A thermometric titrimetry study of Fe 3+/S0CN − and Ag +/SCN − systems

Abstract

Thermometric titrimetry data for the Fe 3+/SCN − system show that, for a titrate concentration in the range 0.0020–0.0024 mol dm −3 and a titrant concentration of 0.1000 mol dm −3, the measured molar reaction heat corresponding to the first end-point formation is −4.42 ± 0.52 kJ mol −1 and the corresponding mean mole ratio factor, n Fe 3+ / n SCN − is 1.04 ± 0.04. However, for titrate concentrations in the range 0.0010–0.0020 mol dm −3, this factor is less than unity but progressively approaches unity as the titrant concentration nears 0.0020 mol dm −3. This phenomenon is explained in terms of a thermal bleaching effect and is demonstrated by the use of an inhibitor in these thermometric titrations. Al 3+ and Mn 2+ cause no measurable interference effect in the Fe 3+/SCN − thermometric titration. A thermometric titration with Ag + (0.0007–0.0030 mol dm −3) as titrate and SCN − (0.1000 mol dm −3) as titrant reveals one end-point-the corresponding measured molar reaction heat is −86.65 ± 3.85 kJ mol −1 and n Ag + / n SCN − is 0.97 ± 0.02. Al 3+ causes no measurable interference effect in this titration. The overall thermoanalytical data obtained for these two systems suggest that thiocyanate can be used as a reagent for the determination of Fe 3+ and Ag + in aqueous solution by thermometric titrimetry.